Vermiculite for enhancement of barite stability in water-based mud at elevated temperature

Analysis of the Impact of Vermiculite on Hematite-Based Cement Systems

Heavyweight oil-well cement systems are designed for isolating intervals and supporting the casing at deeper depths where high temperatures and pressures are encountered. The cement slurry should have adequate rheology to ensure efficient placement. Additionally, the hardened cement sheath should be homogeneous with lower porosity and permeability, higher strength, and sufficient flexibility. The effect of vermiculite on hematite-based cement samples has been investigated. The methodology and testing were based on the American Petroleum Institute standards and other recognized recommendations. Fluid properties were characterized by their rheology, while petrophysical and mechanical properties were used to analyze the properties of hardened cement specimens. The vermiculite was used in concentrations of 0.25, 0.5, 1, and 2% by weight of cement (BWOC). The slurries were cured at 3000 psi and 292 °F in cubic and cylindrical molds for 24 h. The results indicate that using 1% BWOC of vermiculite yields the best cement properties. It minimizes the settling of hematite particles to a very low value compared to the base cement as shown by the method of density variation and confirmed by nuclear magnetic resonance. Compared to the base cement slurry, the slurry of 1% BWOC of vermiculite has desirable rheology in terms of plastic viscosity and gel strength. The incorporation of 1% BWOC improves the strength of the cement sheath by 50.7% for the compressive strength and 65% for the tensile strength. Adding 1% vermiculite reduces the permeability and porosity of the cement by 45.8 and 43.5% compared to the control cement. In addition, the 0.7% vermiculite cement is more flexible than the control cement in terms of the elastic properties represented by lower Young's modulus (a reduction of 33%) and higher Poisson's ratio (an increase of 2%).